Treatment (tx) patterns and clinical outcomes for patients (pts) with de novo versus recurrent HER2+ metastatic breast cancer (MBC).

523 Background: Use of adjuvant trastuzumab (T) in pts with HER2+ early breast cancer is associated with decreased recurrence. As fewer patients relapse, the proportion of pts with de novo metastatic disease in the first-line (1L) setting will increase, which could have implications for the design/interpretation of results from HER2+ MBC trials. To date, little data exist on potential differences in prognosis and outcomes between pts with recurrent vs de novo HER2+ MBC. Methods: registHER is an observational cohort of pts with HER2+ MBC diagnosed ≤6 mo from enrollment and followed until death, disenrollment, or June 2009 (median follow-up: 27 mo). Demographics and 1L tx patterns (using descriptive analyses), as well as clinical outcomes (median PFS and OS estimated by Kaplan-Meier method) were examined for pts with de novo vs recurrent HER2+ MBC. De novo was defined as disease-free interval (DFI) between initial and metastatic diagnosis ≤90 days; recurrent was defined as DFI >90 days. Cox regression analy...